Since I read that NPC in
Original Sin react if they notice you( the hero) (try to) steal their belongings I'm absolutely sure if you kill a NPC other NPC's that see you killing or have a relationship with that killed NPC will become very angry and/or start to attack you ... and if it's a merchant you can't trade with them etc etc .... !
It's indeed the best that killing (innocent) NPC's can have very heavy penalties ! I Hope your hero must be at least a overpowered hero to survive all attacks after killing many NPC's !
In DD you also can kill NPC's, even those who can offer you a quest ! So if it's simular in D:OS, think twice before you plan to kill a NPC !!
